Method for providing home agent geographic redundancy via a service redundancy protocol

ABSTRACT

Methods and systems for providing redundancy in servicing packet data communications within wireless mobile data networks are disclosed. More particularly, the method and system provide a redundant Home Agent with the ability to assume the role of the primary Home Agent in the event of a primary Home Agent network, software, or other failure. The redundancy allows the Home Agent services to remain functional even in the event of a failure of one of the Home Agents in the redundant group, which may be composed of one or more Home Agents. The Home Agents can use a service redundancy protocol which is composed of messages that are sent between the redundant group of Home Agents. The messages allow the Home Agents to, for example, back up call session information, check on the status of one another, and share priority information.

BACKGROUND OF THE INVENTION

The present invention relates to servicing calls in wireless mobile datanetworks. More particularly, this invention relates to providingredundancy in the servicing of packet data communications by Home Agentswithin wireless mobile data networks.

Wireless networks provide users with data without the need for a wiredline tethering the user to a certain location. A wireless network istypically composed of a mobile device, base stations, and a supportinginfrastructure. The mobile device can be, for example, a cell phone, aPDA, or a computer with wireless capabilities. These mobile devicesinteract with base stations that transmit and receive data. The basestations can further be connected to a network infrastructure thatconnects to the public switched telephone network (PSTN), the Internet,and/or other communication networks.

While cellular wireless communication systems were originally designedto transmit voice communications, increasingly these networks have beenmodified to also support data communications, such as packet based datacommunications. Mobile IP, a form of packet based data communication,enables mobile devices to change where they are connecting to theInternet without changing their Internet protocol (IP) address. Variousagents assist in the transmission of packets from a mobile device to theInternet. A Home Agent performs the mobility management functions neededfor IP communications on behalf of the mobile device. Mobile devices getthe Home Agent address either through a static configuration, where theIP address of the Home Agent is hard-coded in the mobile device, orthrough a mobile IP registration process.

When a registration process is used, a server is responsible forassigning Home Agents to mobile devices. In either the static assignmentor the server registration of a mobile device with a Home Agent, it isimportant that the assigned Home Agent is fully functional. Therefore,it is highly desirable to provide redundancy so that a fullyfunctionally Home Agent is always available for a mobile device.

SUMMARY OF THE INVENTION

In accordance with the present invention, techniques and systems forproviding redundancy in the servicing of packet data communicationswithin wireless mobile data networks are provided. More particularly,techniques and systems where a first Home Agent can initiate aswitchover to a second Home Agent to service existing and future packetdata communications on a network are provided.

Thus, in accordance with the present invention, certain embodimentsfeature a first Home Agent acting as a primary Home Agent, a second HomeAgent communicating with the first Home Agent, a communication linkcoupling the first and second Home Agent, the first Home Agent sending aHello Message to the second Home Agent, the Hello Message containingsystem attributes, the first Home Agent sending a Service CheckpointMessage to the second Home Agent which provides information used toperform as the primary Home Agent, and the second Home Agent able, inresponse to at least one of the Hello Message and the Service CheckpointMessage, to transition to become the primary Home Agent.

Further in accordance with the present invention, certain embodimentsfeature a method for sending a Hello Message containing systemattributes from a first Home Agent to a second Home Agent, sending aService Checkpoint Message from the first Home Agent acting as a primaryHome Agent to the second Home Agent, wherein the Service CheckpointMessage contains information used to perform as the primary Home Agent,and transitioning the second Home Agent to the primary Home Agent.

Still further in accordance with the present invention, certainembodiments feature a first mechanism for providing a primary HomeAgent, a second mechanism for providing a second Home Agent, a mechanismfor communicating between the first means and the second mechanism, thefirst mechanism sending a Hello Message to the second mechanism, theHello Message containing system attributes, and the first mechanismsending a Service Checkpoint Message to the second mechanism providinginformation used to perform as the primary Home Agent, wherein thesecond mechanism transitions to become the primary Home Agent.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other advantages of the present invention will be apparentupon consideration of the following detailed description, taken inconjunction with accompanying drawings, in which like referencecharacters refer to like parts throughout, and in which:

FIG. 1 is a schematic diagram of a network that is capable oftransmitting data in accordance with certain embodiments of the presentinvention;

FIG. 2 is a schematic diagram illustrating switchover message flow inaccordance with certain embodiments of the present invention;

FIG. 3 is a schematic diagram illustrating checkpoint message flow inaccordance with certain embodiments of the present invention;

FIG. 4 is a schematic diagram illustrating a manual switchover inaccordance with certain embodiments of the present invention;

FIG. 5 is a schematic diagram illustrating a single Home Agentinitialization in accordance with certain embodiments of the presentinvention;

FIG. 6 is a schematic diagram illustrating a dual Home Agentinitialization in accordance with certain embodiments of the presentinvention;

FIG. 7 is a schematic diagram illustrating a primary to backupswitchover due to a primary failure in accordance with certainembodiments of the present invention;

FIG. 8 is a schematic diagram illustrating a backup to primaryswitchover due to a backup failure in accordance with certainembodiments of the present invention;

FIG. 9 is a schematic diagram illustrating a backup to primaryswitchover due to a redundancy link failure in accordance with certainembodiments of the present invention;

FIG. 10 is a schematic diagram illustrating a primary to backupswitchover due to a BGP monitor failure in accordance with certainembodiments of the present invention; and

FIG. 11 is a schematic diagram illustrating a primary to backupswitchover due to an AAA server monitor failure in accordance withcertain embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with the present invention, systems and techniques forproviding redundancy in the servicing of packet data communicationswithin wireless mobile data networks are disclosed. More particularly,this invention proposes a technique for providing a redundant Home Agentwith the ability to assume the role of the primary Home Agent in theevent of a primary Home Agent network or software failure. Theredundancy allows the Home Agent services to remain functional even inthe event of a failure of one of the Home Agents in the redundant group,which may be composed of one or more Home Agents. The Home Agents can belocated in geographically separate areas to ensure that a network outageevent in one geographic area does not cause subscriber services to beimpacted in another area.

FIG. 1 illustrates a system 150 that composes a network diagram inaccordance with certain embodiments of the present invention.Illustrated system 150 contains Internet 110, a Border Gateway Protocol(BGP) Router 112, an Authentication, Authorization, and Accounting (AAA)Server 114, a Home Agent (HA#1) 116, a Home Agent (HA#2) 118, a PacketData Switched Network (PDSN) Router 120, a PDSN Network 122, and aredundancy link 124. As may be appreciated by one skilled in the art,system 150 may contain additional Routers, Home Agents, and Servers asis needed in a network to provide the level of service desired.Generally speaking, BGP is a system routing protocol that is commonlyused to exchange routing information for the Internet between Internetservice providers. BGP Router 112 may be used to propagate InternetProtocol (IP) information throughout the routing domain and Internet110.

As illustrated, AAA Server 114 can interact with HA#1 116 and HA#2 118to handle mobile device requests for access to network resources. Insome embodiments, AAA Server 114 communicates with a RemoteAuthentication Dial-In User Service (RADIUS) Server to authenticate andauthorize access to system resources. Illustrated HA#1 116 is theprimary Home Agent and actively handles IP communications, while HA#2118 is a backup Home Agent. As shown, HA#1 116 and HA#2 118 areconnected by a redundancy link 124 that provides a channel for passinginformation and allows the two Home Agents to switch states. The twoHome Agents, HA#1 116 and HA#2 118, are connected to PDSN Router 120.PDSN Router 120 may forward data packets through PDSN Network 122 andeventually to the mobile device requesting the data.

In certain embodiments of the present invention, a pair of Home Agentsmay be configured in a primary/backup configuration. In FIG. 1, theprimary Home Agent, HA#1 116, can provide Home Agent services duringnormal operating conditions. Likewise, the backup Home Agent, HA#2 118,can provide Home Agent services during failure conditions. When a HomeAgent is providing services it is considered “Active,” and when the HomeAgent is not providing services it is considered “Standby.” Aninter-Home-Agent communication channel, for example redundancy link 124,may be used to allow the Home Agents to communicate to determine thestate of the Home Agents. The Home Agents may also communicate bysending packets to one another through the existing networkinfrastructure. In some embodiments of the invention, the “Standby” HomeAgent may not switch to “Active” unless a failure is detected. In otherembodiments, the Home Agents may switched manually for performing, forexample, maintenance or upgrades to one of the Home Agents.

In some embodiments of the present invention, the service redundancyprotocol used by the Home Agents is a networking protocol based on atransfer control protocol (TCP) that can provide a communication channelbetween a primary and a backup Home Agent. The communication channel mayallow the Home Agents to determine the peer Home Agent state, tovalidate peer Home Agent configuration, and to synchronize subscribersession information. In certain embodiments, a service redundancyprotocol (SRP) can be implemented as a centralized control/distributedsession model with a SRP-Manager handling various aspects of thecommunication. The SRP-Manager can be a single hardware or softwareprocess that reads incoming and forms outgoing SRP control messagesincluding a Hello message and various configuration validation messages.The SRP-Manager can also be responsible for determining theActive/Standby state of the Home Agent.

In some embodiments, multiple processes called SRP-Session Managers actas distributed agents and communicate subscriber session information tothe redundant Home Agent peer. The peer SRP-Session Managers on theredundant Home Agent may be responsible for receiving this informationand creating a redundant session for use in the event of a switchover.The SRP-Manager can communicate Home Agent state and SRP protocolconfiguration information to the SRP-Session Managers. This informationcan provide each SRP-Session Manager with the ability to contact theremote Home Agent and synchronize the current subscriber sessionsthrough the use of service checkpoint messages.

In certain embodiments of the present invention, SRP Hello Messages aresent by both Home Agents in a redundant grouping. These messages may besent at a periodic interval, randomly, or based on conditions configuredby an administrator. The Hello Messages can be used to determine thestate of the remote Home Agent and to verify communication with theremote Home Agent. In some embodiments, if the Standby Home Agent hasnot received a valid SRP Hello Message from its peer within adead-interval, the Home Agent can assume the Active Home Agent is notfunctioning, and can transition to Active and begin processingsubscriber sessions.

The Hello Message may contain system attributes such as: Home Agentstate, Peer State, Peer Role, Hello Interval, Priority, PriorityTiebreaker, and BGP modifier. The attributes may be appended to a TCPheader and the attributes may be sized in terms of bits, and meaningscan be assigned to bit combinations according the needs of the network.The Home Agent state can be the current state of the Home Agent sendingthe message. The Peer State can be the last known state of a peer HomeAgent. The Peer Role can be the role configured for the Home Agent(e.g., primary, backup, etc.). The Hello Interval can be a user-set timeperiod between adjacently sent Hello Messages. The Priority can be aweight assigned to a Home Agent for use in operation. The PriorityTiebreaker can be a second attribute used to determine which Home Agentshould transition to Active in the case of identical priority. The BGPmodifier can be an attribute used to determine how to route messagesfrom BGP router 112.

In some embodiments of the present invention, there are SRPConfiguration Validation Messages. The Active Home Agent sends the SRPConfiguration Validation Message to the Standby Home Agent. Thesemessages may contain configuration information that allows the StandbyHome Agent to determine if it is properly configured to assume the roleof Active Home Agent. The SRP Configuration Validation Message may allowfor configuration error checking, and verification that the peer HomeAgent is compatible. If an error is determined to exist, the StandbyHome Agent can produce an alarm so that the network operator is notifiedof the potential problem. The Home Agent may also maintain aconfiguration conflict notification mechanism to identify potentialproblems between peer Home Agents to an operator before a switchingevent occurs.

The SRP Configuration Validation Messages may contain attributes suchas: Message Type, Home Agent Configuration, and Home Agent State. TheMessage Type can be the category of configuration message. Some examplesof categories of configuration messages are loopback interfaceconfiguration, IP pool configuration, Home Agent Service IP Address,Home Agent Service configuration, and Home Agent Authentication,Authorization, and Accounting (AAA) probe configuration. The Home AgentConfiguration can be the configuration parameters for the selectedcategory of message. The Home Agent State can be the current state ofthe Home Agent sending the message.

In certain embodiments of the present invention, there are SRP ServiceCheckpoint Messages. The Checkpoint Messages contain data that maydescribe each subscriber session being processed by the Active HomeAgent and can contain fields to indicate which session the data pertainsand whether to overwrite a session already stored on the Standby HomeAgent. The Checkpoint Messages can create/delete redundant sessions onthe Standby Home Agent. The messages can also periodically updatesubscriber session statistics on the Standby Home Agent. The CheckpointMessages may contain all the information needed to recreate a call onthe Standby Home Agent if the Standby Home Agent were to transition toan Active Home Agent. Another Checkpoint Message may be used toinvalidate an existing session (i.e., this message is sent to theStandby Home Agent when a call is terminated on the Active Home Agent).

In some embodiments, the primary and backup Home Agents, illustratedHA#1 116 and HA#2 118 respectively, are configured with common loopbackinterface routes and IP Pool information. The Home Agent services run onthese loopback interface routes. The loopback routes may be advertisedthroughout the IP routing domain, in certain embodiments, through theuse of a dynamic routing protocol on the Active Home Agent. In the eventof a failure, for example, the Standby Home Agent transitions to Activeand begins advertising the loopback and IP Pool routes of the formerlyActive Home Agent. This may allow other elements in the network totransition to communicating with the previously Standby Home Agentwithout service interruption.

In order to preserve existing subscriber sessions during a switchoverevent, in certain embodiments, the Home Agents send messages to eachother during operation. The messages may allow the Standby Home Agent toresume a session in the event that the Home Agent transitions to Active.In some embodiments, the Active Home Agent may monitor the followingitems to detect a possible failure: 1) dynamic routing peerconnectivity; 2) AAA server connectivity; 3) Standby Home Agentconnectivity; 4) internal software state. In the event one of theseitems fails, the Active Home Agent may initiate a switchover eventallowing the Standby Home Agent to transition to Active and avoid aservice interruption to any existing or new subscribers.

FIG. 2 illustrates the interactions between a Mobile Node 210, a ForeignAgent 212, a Home Agent #1 214, and a Home Agent #2 216 in a switchoverevent in accordance with certain embodiments of the present invention.As shown in this example, Active Home Agent #1 214 advertises its IPPool and loopback interface routes into the Border Gateway Protocol(BGP) router in step 218. Standby Home Agent #2 216 does not advertisethe common loopback and IP pool routes to the BGP router in step 220. Atsome later point in time, Home Agent #1 214 receives a Mobile IPregistration request from Foreign Agent 212. When Home Agent #1 214replies to the request, a call is established in step 222. Subscriberdata can then flow for some time from Mobile Node 210 to Home Agent #1214.

According to some embodiments of the invention, data from Home Agent #1214 is backed up on Home Agent #2 216 at certain times in step 224. Thebackup of information may occur because a preset duration timer hasexpired or because a predefined event triggers the backup. The backed-upinformation includes the data necessary to either continue a call, torecreate a call on another Home Agent, or to refresh any other ancillarydata desired. If a switchover event occurs while a call is Active (instep 226), Home Agent #1 214 may revert to Standby withdrawing thecommon loopback and IP Pool routes from the BGP router in step 228. Thisallows Home Agent #2 216 to advertise its IP Pool and loopback routes tothe BGP router in step 230. When the BGP router learns of the change, itbegins forwarding traffic to Home Agent #2 216 in step 232 and thesubscriber data begins flowing through Home Agent #2 216. Because HomeAgent #1 214 and Home Agent #2 216 use a common loopback serviceaddress, other network devices may not be aware of any switchover instep 234.

FIG. 3 illustrates SRP Service Checkpoint Message flow in accordancewith certain embodiments of the present invention. The message flowinteractions involve a Foreign Agent #1 310, a Foreign Agent #2 312, aHome Agent #1 314, and a Home Agent #2 316. As shown, Home Agent #1 314receives a Mobile IP registration request from Foreign Agent 310. Inresponse, Home Agent #1 314 sends a Mobile IP registration reply toinitiate a new session and a call is established 318. After the sessionpasses the checkpoint defined duration timer, the session can be backedup on the Standby Home Agent in step 320. The checkpoint duration timercan be set to a value, such as 60 seconds, as shown in FIG. 3. Event 320may include Home Agent 314 sending a Service Checkpoint Message and aService Statistics Message to Home Agent #2 316. In some embodiments, aService Checkpoint Message may be sent without a Service StatisticsMessage.

At some point in time, Foreign Agent #1 310 initiates a handoff toForeign Agent #2 312 in step 322. Foreign Agent #1 310 may send a MobileIP registration request to Home Agent 314 and Home Agent #1 314 may sendback a Mobile IP registration reply. The handoff event 322 may triggerthe generation of a Service Checkpoint Message in step 324 to update theinformation on the call for Home Agent #2 316. When the call isterminated in step 326 and Mobile IP deregistration request is sent toHome Agent #1 314, Home Agent #1 314 replies with a Mobile IPderegistration acknowledgement. Home Agent #1 314 may then send HomeAgent #2 a Service Checkpoint Invalidate Message to prompt Home Agent #2316 to remove the information for the call from its system. The ServiceCheckpoint Invalidate Message may ensure a terminated call is notreinstated possibly causing service disruptions or tying up networkresources if Home Agent #2 316 transitions to an Active state.

FIG. 4 illustrates a manual switchover event involving a Home Agent #1410 and a Home Agent #2 412 in accordance with certain embodiments ofthe invention. As shown in this example, Home Agent #1 410 is in anActive state with certain priority and BGP modifier attributes ashighlighted in step 414. These attributes may be sent in a Hello Messageto other Home Agents so the status of the various Home Agents on thenetwork is known to each other. As shown, Home Agent #2 412 is in aStandby state and has a priority of 100 and a BGP modifier of 1 in step416. In some embodiments, the Hello Messages contain routing attributeinformation for deciding Init state transitions.

When Home Agent #1 410 initiates a manual switchover event 418, newcalls may be rerouted to Home Agent #2 412, sent to one or more otherHome Agents (not shown), or rejected depending on the embodiment of theinvention. As shown, Home Agent #1 410 sends Checkpoint Messages to passbackup information to Home Agent #2 412. In step 420, Home Agent #1 410continues checking the calls it is handling until the calls are finishedor a switchover timeout is reached. At about the same time, Home Agent#2 412 updates its information for the calls and refreshes itsconfiguration settings from the backup information it is receiving fromHome Agent #1 410 in step 422. When Home Agent #1 410 is no longerservicing any calls, it can transition to Standby and notify Home Agent#2 412 through a Hello Message in step 424 that it has done so. TheHello Message alerts Home Agent #2 412 that Home Agent #1 410 haschanged states and Home Agent #2 412 transitions to an Active state instep 426. In certain embodiments, Home Agent #2 412 then sends a HelloMessage to Home Agent #1 410 to indicate it is in the Active state instep 428.

FIG. 5 illustrates a single Home Agent initialization involving HomeAgent #1 510 and Home Agent #2 512 in accordance with certainembodiments of the present invention. In this example, Home Agent #2 512is running in the Active state in step 514 and Home Agent #1 510 comesonline in an Init state. Home Agent #1 510 proceeds to send a HelloMessage to Home Agent #2 512 in step 516. Home Agent #2 512 receives theInit Hello Message from Home Agent #1 510 containing state, priority,and BGP modifier information of Home Agent #1 510 in step 518. HomeAgent #2 512, upon evaluating the Hello Message, remains Active andsends a Hello Message with its Active state to Home Agent #1 510 in step520. Home Agent #1 510 receives the Hello Message in step 522,transitions to Standby, and based upon the Hello Message updates its BGProuting attribute from zero to one in step 524. At a later point intime, Home Agent #1 510 sends a Hello Message to Home Agent #2 512, butno state change is required in step 526. Home Agent #2 512 can remainActive and handling the calls because Home Agent #1 510 has confirmed itis in the Standby state.

FIG. 6 illustrates a dual Home Agent initialization in accordance withcertain embodiments of the present invention. As shown in this example,a Home Agent #1 610 and a Home Agent #2 612 are initialized upon comingonline. Home Agent #1 610 and Home Agent #2 612 may then exchange HelloMessages with state, priority, and BGP modifier information in steps 614and 616. Home Agent #2 612 receives the Hello Message from Home Agent #1610 in step 618 and based on a comparison of one or more routingattributes, such as priority and BGP modifier, transitions to Standby instep 620. Home Agent #1 610 has a lower priority and BGP modifier thanHome Agent #2 612. The BGP modifier may be used initially to determinewhich Home Agent should become Active and the priority may then be usedif more than one Home Agent shares the same BGP modifier value.

As illustrated, after a comparison and transition, Home Agent #2 612notifies Home Agent #1 610 of its Standby state. When Home Agent #1 610receives notice of the Standby state of Home Agent #2 612 in step 622,it can transition to Active in step 624. In certain embodiments, HomeAgent #1 610 remains in the Init state after the comparison of one ormore routing attributes because the routing attribute rules do notspecify that the Home Agent transition into Standby. In otherembodiments, Home Agent #1 610 transitions to Active based on thecomparison, and Home Agent #2 612 transitions to Standby after learningHome Agent #1 610 is Active. In still other embodiments, the Home Agentsmay transition based on the outcomes of the comparisons and then checkthe outcome with further Hello Messages. Upon receiving confirmation ofthe Active state from Home Agent #1 610, Home Agent #2 612 can remain inStandby state in step 626.

FIG. 7 illustrates a primary Home Agent failing and the subsequentswitchover to a backup Home Agent in accordance with certain embodimentsof the present invention. As shown in this example, a Home Agent #1 710is Active in step 712 and a Home Agent #2 714 is Standby in step 716with Hello Messages being passed at regular intervals. At some point intime, Home Agent #1 710 fails and stops sending Hello Messages in step718. After a specified dead-interval where Home Agent #2's HelloMessages go unanswered, Home Agent #2 714 initiates a switchover to anActive state 720. Upon transitioning to Active, Home Agent #2 714 beginsadvertising the loopback and IP pool routes to the routing domain instep 722. An Authentication, Authorization, and Accounting (AAA) Server(shown in FIG. 1 as 114) may enable services for Home Agent #2 714 soHome Agent #2 714 can then begin taking calls. At some later point intime, Home Agent #1 710 recovers and sends a Hello Message with an Initstate to Home Agent #2 714 in step 724. Home Agent #1 710 receives theHello Message from Home Agent #2 714 with an Active state. Afterevaluating the information received in the Hello Message, Home Agent #1710 transitions to Standby and updates its BGP modifier to two in step726. The new BGP modifier helps to determine how to route messages andmay help establish which Home Agent is going to transition to Active.

FIG. 8 illustrates a backup Home Agent failing and the subsequentswitchover to a primary Home Agent in accordance with certainembodiments of the present invention. FIG. 8 may be considered acontinuation of the situation presented in FIG. 7. As shown in thisexample, a Home Agent #1 810 is in a Standby state in step 812 and aHome Agent #2 814 is in an Active state in step 816. Hello Messages maythen be passed between the Home Agents at regular intervals. At somepoint in time, Home Agent #2 814 fails and stops sending Hello Messagesin step 818. Home Agent #1 810 may continue sending Hello Messages untila specified dead-interval ends, at which point Home Agent #1 810initiates a switchover to Active in step 820. Upon transitioning toActive, Home Agent #1 810 begins advertising the loopback and IP poolroutes to the routing domain. Home Agent #1 810 may also establishcontact with Authentication, Authorization, and Accounting (AAA) Serverto enable call verification services. After advertising the loopback andIP pool routes and accessing the AAA server, Home Agent #1 810 can begintaking calls in step 822. At some later point in time, Home Agent #2 814recovers and sends a Hello Message with an Init state in step 824. HomeAgent #2 814 receives a Hello Message from Home Agent #1 810 with anActive state and Home Agent #2 814 transitions to Standby in step 826.Home Agent #2 also updates its BGP modifier to three after receiving theHello Message from Home Agent #1 810.

FIG. 9 illustrates a backup Home Agent to a primary Home Agentswitchover due to a redundancy link failure in accordance with certainembodiments of the present invention. As shown in this example, a HomeAgent #1 910 is in the Standby state in step 912 and a Home Agent #2 914is in the Active state in step 916. Hello Messages may be passed betweenthe Home Agents at regular intervals until communication between HomeAgent #1 910 and Home Agent #2 914 is lost due to a link failure in step918. Home Agent #1 910 detects that Home Agent #2 914 has not sent aHello Message within the dead-interval, and may initiate a switchover toan Active state in step 920. At the same time, Home Agent #2 914continues to be Active in step 922.

In certain embodiments of the invention, Home Agent #2 914 remains thepreferred Home Agent in the routing domain because the BGP modifieradvertised in the network is lower with Home Agent #2 914 than with HomeAgent #1 910. In other embodiments, Home Agent #1 910 may become thepreferred Home Agent upon switching to Active when the link goes down.In step 926, when Home Agent #1 910 receives a Hello Message from HomeAgent #2 914, the BGP modifier may be used to determine which Home Agentshould transition to Standby. In this example, Home Agent #1 910transitions back to Standby because Home Agent #2 914 is still preferredin the routing domain. After transitioning to Standby, Home Agent #1 910sends a Hello Message to Home Agent #2 914. Home Agent #2 914 receivesthe Hello Message which includes information that Home Agent #1 910transitioned to a Standby state. Home Agent #2 914 may update its ownBGP modifier if needed in step 928.

FIG. 10 illustrates a primary Home Agent to a backup Home Agentswitchover due to a BGP monitor failure in accordance with certainembodiments of the present invention. As shown in this example, a HomeAgent #1 1010 is in the Active state in step 1012 and a Home Agent #21014 is in the Standby state at step 1016. Hello Messages may be passedbetween the Home Agents at regular intervals. In certain embodiments,the Home Agents check BGP router 112 (as shown in FIG. 1) to ensure thatit is still functioning. In step 1018, Home Agent #1 1010 checks the BGProuter and finds it is not functioning. The checking mechanism may be atimer which resets after receiving a packet and monitors traffic sentfrom the BGP router. In this case, if the timer reaches a predeterminedvalue without seeing traffic from the BGP router, the BGP router issuspected to be inactive or in a failure mode. Home Agent #1 1010 maytransition to Standby to give Home Agent #2 1014 a chance at functioningin the network. To initiate Home Agent #2 1014 transitioning to anActive state, Home Agent #1 1010 sends a Hello Message to Home Agent #21014. Home Agent #2 1014 receives the Hello Message, which includes suchattributes as: current state information, priority information, and BGProuting information, and in response, transitions to an Active state instep 1020. Home Agent #2 1014 then begins advertising the loopback andpool routes into the routing domain so it can begin taking calls in step1022. Home Agent #2 1014 may send Home Agent #1 1012 a Hello Messagewhich reinforces that Home Agent #1 1010 will remain in the Standbystate in step 1024.

FIG. 11 illustrates a primary Home Agent to backup Home Agent switchoverdue to an AAA server monitor failure in accordance with certainembodiments of the invention. As shown in this example, a Home Agent #11110 is in the Active state in step 1112 and a Home Agent #2 1114 is inthe Standby state in step 1116. The two Home Agents may trade HelloMessages at regular intervals for some time until an AAA RADIUS Server1118 is no longer reachable by Home Agent #1 1110 in step 1120. HomeAgent #1 1110 may continue to send out a number of RADIUS server probesthat check the status of AAA RADIUS Server 1118. In certain embodimentsa predefined number of attempts may be specified, while in otherembodiments a dead-interval may be specified. If Home Agent #1 1110 doesnot receive a valid response from the AAA server after trying accordingto the selected, predetermined method, Home Agent #1 1110 may transitionto Standby in step 1122.

As shown, if Home Agent #1 1110 transitions to Standby, a Hello Messageis received by Home Agent #2 1114 from Home Agent #1 1110 noting thechange in state and BGP modifier. Home Agent #1 1110 may include an AAAserver monitoring mechanism which marks AAA RADIUS Server 1118 as downafter the Home Agent #1 1110 exhausted a specified number of tries toreach the AAA RADIUS Server. This AAA server monitoring mechanism mayupdate the BGP modifier if the mechanism detects that the AAA server isdown. A Hello Message prompting Home Agent #2 1114 to transition to anActive state is sent from Home Agent #1 1110 in step 1124. Home Agent #21114, in step 1126, begins advertising identification information, whichmay include IP loopback and pool routes, into the routing domain andenables AAA services so that calls can be taken. In step 1128, HomeAgent #2 1114 begins sending authorization probe message to the AAARADIUS server. In certain embodiments, if the RADIUS probe message isaccepted, Home Agent #2 1114 may send a Hello Message to Home Agent #11110 to confirm Home Agent #1 1110 can remain in Standby in step 1130.In other embodiments, the Hello Message from Home Agent #2 1114 may besent, after a period of time which is predetermined, to Home Agent #1 toconfirm Home Agent #2 is still operational and Active.

Other embodiments, extensions, and modifications of the embodimentspresented above are within the understanding of one versed in the artupon reviewing the present disclosure. Accordingly, the scope of thepresent invention in its various aspects should not be limited by theexamples presented above. The individual aspects of the presentinvention, and the entirety of the invention should be regarded so as toallow for design modifications and future developments within the scopeof the present disclosure.

1. A system for providing communication between Home Agents comprising:a first Home Agent acting as a primary Home Agent; a second Home Agentcommunicating with the first Home Agent; a communication link couplingthe first and second Home Agent; the first Home Agent being able to senda Hello Message to the second Home Agent, the Hello Message containingsystem attributes; the first Home Agent being able to send a ServiceCheckpoint Message to the second Home Agent which provides informationused to perform as the primary Home Agent; and the second Home Agentbeing able, in response to at least one of the Hello Message and theService Checkpoint Message, to transition to become the primary HomeAgent.
 2. The system of claim 1, wherein the communication link is aredundancy link.
 3. The system of claim 1, wherein the Hello Message andthe Service Checkpoint Message are formatted in accordance with aTransfer Control Protocol (TCP) based networking protocol.
 4. The systemof claim 1, wherein the second Home Agent transitions to the primaryHome Agent based on information in the Hello Message.
 5. The system ofclaim 1, wherein the system attributes of the Hello Message are HomeAgent state, Priority, and BGP modifier.
 6. The system of claim 1,wherein the second Home Agent after transitioning to the primary HomeAgent advertises identification information of the first Home Agent. 7.The system of claim 6, wherein the identification information includesIP Pool and loopback interface routes.
 8. A method for providingcommunication between Home Agents comprising: sending a Hello Messagecontaining system attributes from a first Home Agent to a second HomeAgent; sending a Service Checkpoint Message from the first Home Agentacting as a primary Home Agent to the second Home Agent, wherein theService Checkpoint Message contains information used to perform as theprimary Home Agent; and transitioning the second Home Agent to theprimary Home Agent.
 9. The method of claim 8, wherein the communicationoccurs through a redundancy link.
 10. The method of claim 8, furthercomprising sending the Hello Message and the Service Checkpoint Messageusing a Transfer Control Protocol (TCP) based networking protocol. 11.The method of claim 8, wherein the transitioning step is based oninformation in the Hello Message.
 12. The method of claim 8, wherein thesystem attributes of the Hello Message are Home Agent state, Priority,and BGP modifier.
 13. The method of claim 8, further comprisingadvertising identification information of the first Home Agent after thesecond Home Agent transitions to the primary Home Agent.
 14. The methodof claim 13, wherein the identification information includes IP Pool andloopback interface routes.
 15. A system for providing communicationbetween Home Agents comprising: a first means for providing a primaryHome Agent; a second means for providing a second Home Agent; a meansfor communicating between the first means and the second means; thefirst means sending a Hello Message to the second means, the HelloMessage containing system attributes; and the first means sending aService Checkpoint Message to the second means providing informationused to perform as the primary Home Agent, wherein the second meanstransitions to become the primary Home Agent.
 16. The system of claim15, wherein the communication means is a redundancy link.
 17. The systemof claim 15, wherein the Hello Message and the Service CheckpointMessage are a Transfer Control Protocol (TCP) based networking protocol.18. The system of claim 15, wherein the second means transitions to theprimary Home Agent based on information in the Hello Message.
 19. Thesystem of claim 15, wherein the system attributes of the Hello Messageare Home Agent state, Priority, and BGP modifier.
 20. The system ofclaim 15, wherein the second means after transitioning to the primaryHome Agent advertises identification information of the first meansthrough the communication means.
 21. The system of claim 20, wherein theidentification information is IP Pool and loopback interface routes.